The disclosure relates to a piston pump for a hydraulic vehicle braking system having the features of the disclosure. The piston pump is provided in particular for producing a braking pressure or for recirculating brake fluid in the direction of a main brake cylinder in traction-controlled hydraulic vehicle braking systems, wherein such pumps are also referred to as recirculation pumps, or for producing a brake pressure in an electrohydraulic, that is to say, external power vehicle braking system, wherein the piston pump can also be used for a slip control system in the latter case. The piston pump can also be referred to as a pump element of a piston pump, in particular a multi-piston pump.
Such piston pumps are known and they conventionally have a pump piston and a pump chamber whose cross-section is congruent with a cross-section of the pump piston, that is to say, it is generally circular. The pump piston can be displaced in the pump chamber in an axial or generally longitudinal direction and can be driven—conventionally with a cam—to carry out a back and forth stroke movement in the longitudinal direction of the pump chamber. As a result of the stroke movement, in a manner known per se, with a suction stroke, fluid, braking fluid in the case of a hydraulic vehicle braking system, is drawn in and displaced with a delivery stroke out of the pump chamber, that is to say, the fluid is conveyed using the piston pump. A throughflow direction of the piston pump is controlled with an inlet valve and an outlet valve which are generally non-return valves. The pump chamber is often also referred to as a cylinder or cylinder bore; it may, for example, be an inner space of a liner which is pressed into a hole of a hydraulic block which receives other hydraulic components of a slip control system, such as solenoid valves, or the pump chamber is formed directly by a hole in such a hydraulic block. The pump chamber may also be formed in a cylinder or a pump housing of the piston pump. The listing is exemplary and not definitive. An example of such a piston pump is disclosed in patent application DE 199 02 018 A1.
For various slip control systems, in particular for an electronic stability program/electronic stability control or an automatic braking system for preventing an approach right up to a vehicle travelling in front or a stationary vehicle or any other obstacle or person, a very rapid response of one, more or all wheel brakes of a vehicle is important, which requires a pump with a large delivery volume. As the delivery pressure increases, that is to say, as the pressure at the outlet of the piston pump increases, a drive torque and a driving power of the piston pump increase. So that the piston pump does not stop as the delivery pressure increases, it requires a drive motor, generally an electric motor, with a correspondingly high torque and great driving power, that is to say, a large and heavy motor. Furthermore, an electronic control device has to be configured for a high electrical power consumption of such a drive motor.